This invention relates to a method for feeding a film in a microfilm reader, for example, and more particularly to a method for winding back a film provided with a leader film wound once around a wind-up reel.
With a known device provided with a cartridge in which a microfilm wound around a reel is accommodated, in a case where it is required to feed or wind back the microfilm, there is used a microfilm to the front end of which a leader film having a width wider than that of the microfilm is attached to prevent the microfilm from being entirely wound up around the reel and to readily be wound off again. One example of the microfilm of this type is shown in FIG. 2 and a picture image 3 and a blipmark or film mark 4 corresponding to the picture image 3 are photographed on the microfilm 1, the front end of which is joined with a leader film 2 through a splicing tape 5.
FIG. 1 is a schematic perspective view of one example of a conventional microfilm reader adapted for applying the method of this invention, and referring to FIG. 1, the microfilm 1 is wound around a reel 10 which is accommodated in a cartridge 11 and a feed-out roller 12 is rotated while being pressed against the leader film 2 at the feed opening of the cartridge 11. The leader film 2 thus fed is transferred and then wound up around an auto-reel 15 for winding up the microfilm 1. A pair of pinch rollers (or odometer rollers) 16 are disposed along the microfilm travelling path so as to clamp the microfilm 1 for assisting the travelling of the microfilm 1. The auto-reel 15 is connected to a drive shaft of an electric motor (M2) 14 which can be driven in a reversible manner at high and low speeds continuously or stepwisely. Under the condition shown in FIG. 1, when the motor 14 is driven, the microfilm 1 is fed or wound back and the picture image information on the microfilm 1 is focused on a screen, not shown, by projecting a light from a light source 17 on the microfilm by the use of a lens unit 18. The focused picture image information is searched, and after the searching operation, an electric motor (M1) 13 is driven at high speed to wind back the microfilm 1 around the reel 10 in the cartridge 11. The motor 13 can also be driven in a reversible manner at high and low speeds continuously or stepwisely. When the leader film 2 reaches the reel 10, the leader film 2 is wound around the outer periphery of the flanged portions 10A and 10B of the reel 10 without being wound around the reel 10 because the leader film 2 has a width wider than the distance between the flanged portions 10A and 10B which is generally substantially equal to the width of the microfilm 1 as best illustrated in FIG. 6A. With the device of the construction described hereinbefore, however, the leader film 2 may be pulled into the gap between the flanged portions 10A and 10B as shown in FIG. 6B because of the large inertia force of the motor (M1) 13 driven at high speed when an excessive tension caused by the friction resistance in a film reader system including the motor (M2) 14 is applied to the microfilm 1. This phenomenon will damage the leader film 2 and make it impossible to smoothly feed again the microfilm 1 from the reel 10, and moreover, this phenomenon will be frequently caused in a case where the whole length of the microfilm used is relatively short and the diameter of the microfilm 1 wound around the reel 10 is considerably smaller than the outer diameter of the flanged portions 10A and 10B of the reel 10.